For processing a workpiece with complex and cubic shape, it is usually necessary to cut from multiple directions simultaneously (with the exception of the bottom side). This is a universal machine tool or five-side working machine. The conventional five-side working machine, in general, has three types: (1) the vertical/horizontal spindle head found in association with a rotary work table for universal changeover of spindle head; (2) the spindle head which comprises two rotary changeover spindles; (3) the spindle head having two-direction (horizontal, vertical) power output ends to match with rotary spindle that can make spindle head changeover by rotation.
Because the spindle head of a conventional universal machine tool must include a universal changeover mechanism, its spindle transmission system is more complex than that of the common machine tool.
Generally the motor and power supply device of a universal spindle head are mounted on the main body of the machine tool and a transmission system comprising some long transmission spindles, gear sets and bevel gears is provided for transmitting power to the main spindle of the spindle head to make the main spindle rotate. The source of power for this universal spindle head engaged in universal changeover is supplied by a main spindle motor and power device so that the spindle head must include a complex clutch and power switchover device in order to switch the power of the motor and power device to lead the spindle head into universal changeover.
Because the spindle heads of conventional universal machine tools have to use the transmission device of a complex structure for leading main spindle in rotation and direction changeover, the complex structure inside the spindle head as well as the transmission spindle of the transmission device and complex gear sets suffer from severe power loss, increasing main spindle vibration and limiting the maximum rotational speed.
In addition, circuits, air pressure, hydraulic pressure and lubrication oil lines used by the spindle head of the conventional universal machine tool are usually exposed out of spindle head so those oil lines are easily polluted and damaged. Further when spindle head is changing over through rotation lines would be swinging in accordance with the movement of spindle head and therefore easily get twisted out of operating condition.